زفر

Arabic zafar (زفر) referred to a metallic oxide — cobalt ore roasted to produce a blue pigment. The word may derive from the Arabic root meaning 'to become blue' or from an older Persian term for cobalt-bearing minerals. Arab alchemists in Baghdad and Damascus were experimenting with metallic oxides by the 800s, and they discovered that roasted cobalt produced a blue so deep and stable it could survive the kiln fires of ceramic glazing.

The pigment traveled east to China, where potters of the Yuan dynasty (1271–1368) imported Persian cobalt to produce the blue-and-white porcelain that became China's most famous export. The cobalt came overland along the Silk Road, from mines in Kashan, Iran. Chinese potters called it 'Mohammedan blue.' The most celebrated Chinese art form depended on a Persian mineral with an Arabic name.

Zaffer traveled west as well. By the 1400s, Italian ceramicists were importing cobalt oxide for maiolica ware, and the word entered Italian as zaffera and then French as safre. Dutch potters in Delft adopted the same pigment in the 1600s to create their iconic blue-and-white tiles. Every version of blue-and-white ceramic in the world traces its color to the same roasted cobalt ore.

English borrowed the word as zaffer (also spelled zaffre) by the 1600s, though the pigment itself was already fading from common knowledge as industrial chemistry replaced alchemical recipes. The word is nearly extinct in modern English. But every piece of blue-and-white pottery in every museum in the world owes its color to the substance it names.